1. Field of the Invention
The present invention relates to a recording apparatus for forming an image in accordance with an image signal or an original image, and particularly to an ink jet recording apparatus and a recording method.
2. Related Background Art
Conventionally, recording apparatuses using a variety of image forming means have been practically used. Among them, an ink jet recording apparatus in particular has gained wide acceptance because it is favorable in the respects of constitution and running costs. The ink jet recording apparatus performs the dot recording by discharging ink droplets through the nozzles of a recording head onto a recording medium. Exemplary of this recording apparatus is a constitution in which a recording head having a row of nozzles with a predetermined width is sequentially scanned for recording in the longitudinal and horizontal directions relative to the recording medium.
The ink jet recording method forms an image by jetting ink droplets directly onto the recording medium in the above way. Unlike the electrophotographic recording method, it has a feature of being able to form an intended image stably because of its smaller number of processes to form the image.
However, there is some instability with the recording of discharging fine ink droplets through the minute nozzles, for example, non-discharge caused by the clogging of ink discharge orifice in the nozzle with contaminants, dusts or thickened ink, mon-discharge caused by the disconnection of the heater for heating the ink in the nozzle, non-discharge caused by ink droplets enclosing capriciously ink discharge orifice of the nozzle, etc., so that white streaks are likely to occur along the main scan (serial scan) direction, whereby there is a risk that a non-defective image can not be produced.
With such a problem, when the number of nozzles is increased up to several hundreds or thousands to speed up the recording, the probability of occurrence of an abnormal nozzle will increase proportionally thereto, and in the current state of the art, the non-defective image is difficult to obtain.
From the standpoint of fabrication of the recording head, it is conventionally requisite that all the nozzles be normal in non-defective heads in order to obtain the non-defective image. But if the number of nozzles is increased up to several hundreds or thousands, the probability of occurrence of defects during fabrication will increase in proportion thereto, resulting in decreased yield of fabrication, whereby it was difficult to manufacture economically in the practicable basis.
Also, even if the non-defective recording head is fabricated, the whole of the recording head will fail in service when one nozzle causes a trouble during use. Hence, there was a problem that if an abnormal nozzle occurs with a recording apparatus having six to eight multi-nozzles, defective printed matter may be produced every time of printing, whereby it is necessary to stop the apparatus to exchange the recording head.
To cope with such problem, it is conceived as a measure that the prevention against the clogging of nozzles is made, a recovery device for effecting the recovery is activated if a nozzle clogging is detected visually, or a recovery operation is incorporated into the print sequence, supposing that the clogging of nozzles may occur.
Also, one solution has been proposed that when the clogging of nozzles occurs during the printing, the overprint is made on the defective part of the image to reduce the influence of clogging (see for example U.S. Pat. No. 4,963,882 and U.S. Pat. No. 4,967,203).
However, with such a solution taken, the probability of occurrence of the clogging of nozzles will decrease, but is not totally reduced to zero, or further no measure has been made in the state of the art against irreversible undischarge, which will occur when contaminants passing through the ink filter at a certain probability may accumulate to clog some nozzles, or when the disconnection of discharge heater for heating the ink happens accidentally or due to the expiration of its span of life.
Also, by executing the recovery operation with a method as disclosed in the above-described U.S. patents, white streaks may be relieved to some extent, but not completely eliminated, whereby it is difficult to say that all the problems have been resolved.
On the other hand, with an image processing technique such as an error diffusion method, and further in a combination with a multi-valued print technique (which adjusts the size of a dot by forming one pixel with the overprint of a few ink droplets of smaller size and depending on the multiplicity of prints), the gradient representation is allowed, and further the provision of some specific color print heads beyond conventional four colors is easy, whereby the multi-color print such as the printing with six to ten colors is possible, with the color reproduction range broadly extended, so that the image representation ability itself with the ink jet print technique has reached a level closer to that of the offset printing.
However, at the practical level, the above problems have not been completely resolved, and the ink jet print technique has not been applied widely although it has many features such as the instant output of computer publishing, no impression creating process, no need of ink mixing, and the wider color reproduction range.
Accordingly, the requirements of offering the non-defective printed matter along with the productivity (speed, continuous operation) and profitability having industrial meanings to the ink jet print technique Rowe not been realized with any of the conventional techniques.